MARKETABLE SECURITIES - Schedule of Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	$ 551.6	$ 545.7
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	304.2	312.2
Fair Value, Inputs, Level 1 [Member] | Mutual Funds and Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	279.7	285.3
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	24.5	26.9
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	247.4	233.5
Fair Value, Inputs, Level 2 [Member] | U.S. Government Issued Debt Securities (Agency and Treasury) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	65.5	46.6
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	43.3	43.9
Fair Value, Inputs, Level 2 [Member] | Asset-Backed Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	18.0	20.0
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	110.3	111.4
Fair Value, Inputs, Level 2 [Member] | Other Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	$ 10.3	$ 11.6